- #1
chaoseverlasting
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There are a couple of things I don't understand about the DA in general and when we use it in the common mode in particular (same input ac voltage to both input terminals). I am using Electronic Circuit and Theory by Louis Nashelsky and Robert Boylstad (p.591 for DA).
When we set the operating point, we do it using DC voltages which sets the values Ic, Ib and Ie.
In the ac analysis, however, we use the values of AC voltages to calculate the voltage across the output resistor. For the re model of the transistor, the value of re in the ac domain is calculated by [tex]r_i=\frac{26mv}{I_b}[/tex] where Ib is the ac current.
However, [tex]r_e=\frac{26mv}{I_e}=\frac{26mv}{\beta I_b}=\frac{r_i}{\beta}[/tex] is calculated using the DC value of Ie.
How is that possible? The DC and AC values of currents are bound to be different, but they are used interchangeably!
I thought that the net current would be the ac+dc values of the current (eg. Ie net=Ie ac + Ie dc).
Sorry for the long post, I couldn't help it.
When we set the operating point, we do it using DC voltages which sets the values Ic, Ib and Ie.
In the ac analysis, however, we use the values of AC voltages to calculate the voltage across the output resistor. For the re model of the transistor, the value of re in the ac domain is calculated by [tex]r_i=\frac{26mv}{I_b}[/tex] where Ib is the ac current.
However, [tex]r_e=\frac{26mv}{I_e}=\frac{26mv}{\beta I_b}=\frac{r_i}{\beta}[/tex] is calculated using the DC value of Ie.
How is that possible? The DC and AC values of currents are bound to be different, but they are used interchangeably!
I thought that the net current would be the ac+dc values of the current (eg. Ie net=Ie ac + Ie dc).
Sorry for the long post, I couldn't help it.